It is the purpose of this study to define the effects of retinoids on carcinogenesis in the tracheal epithelium. To achieve this goal, several areas are being simultaneously investigated. 1) A reproducible model for the study of lung cancer using N-methyl-N-nitrosourea (NMU) or other water soluble carcinogens, in the hamster trachea is being developed. 2) Various retinoids are being tested, using this model, for their ability to modulate the effects of administered carcinogens. 3) Methods for collecting exfoliated cells from the lung are being investigated.